1. Technical Field
This invention relates generally to an apparatus and method for selectively circulating fluid in a well bore. More particularly, the invention relates to a selectively and continually actuatable circulation sub or valve and its method of use in, for example, well bore operations, including drilling, completion, workover, well clean out, coiled tubing, fishing and packer setting.
2. Description of Related Art
When drilling an oil, gas, or water well, a starter hole is first drilled, and the drilling rig is then installed over the starter hole. Drill pipe is coupled to a bottom hole assembly (“BHA”), which typically includes a drill bit, drill collars, stabilizers, reamers and other assorted subs, to form a drill string. The drill string is coupled to a kelly joint and rotary table and then lowered into the starter hole. When the drill bit reaches the base of the starter hole, the rotary table is powered and drilling may commence. As drilling progresses, drilling fluid, or “mud”, is circulated down through the drill pipe to lubricate and cool the drill bit as well as to provide a vehicle for removal of drill cuttings from the borehole. The drilling fluid may also provide hydraulic power to a mud motor. After emerging from the drill bit, the drilling fluid flows up the borehole through the annulus formed by the drill string and the borehole, or the well bore annulus.
During drilling operations, it may be desirable to periodically interrupt the flow of drilling fluid to the BHA and divert the drilling fluid from inside the drill string through a flow path to the annulus above the BHA, thereby bypassing the BHA. For example, the mud motor or drill bit in the BHA tend to restrict allowable fluid circulation rates. Bypassing the BHA allows a higher circulation rate to be established to the annulus. This is especially useful in applications where a higher circulation rate may be necessary to effect good cuttings transport and hole cleaning before the drill string is retrieved. After a period of time, the flow of drilling fluid to the BHA may be reestablished. Redirecting the flow of drilling fluid in this manner is typically achieved by employing a circulation sub or valve, positioned on the drill string above the drill bit.
Typical circulation subs are limited by the number of times they can be actuated in one trip down the borehole. For example, a typical circulation sub may be selectively opened three or four times before it must be tripped out of the borehole and reset. Such a tool operates via the use of a combination of deformable drop balls and smaller hard drop balls to direct fluid flow either from the tool into the borehole annulus or through the tool. As each ball passes through the tool, a ball catcher, positioned at the downhole end of the tool, receives the ball. A drawback to this circulation sub is that the tool may be actuated via a ball drop only a limited number of times, or until the ball catcher is full. Once the ball catcher is full, the tool must be returned to the surface for unloading. After the ball catcher is emptied, the tool may be tripped back downhole for subsequent reuse. Thus, circulation of fluid in the borehole requires repeatedly returning the tool to the surface for unloading and then tripping the tool back downhole for reuse, which is both time-consuming and costly. Furthermore, such circulation subs do not adequately handle dirty fluid environments including lost circulation material, nor do they include open inner diameters for accommodating pass-through tools or obturating members.
Thus, there remains a need for improved apparatus and methods for selectively circulating fluid within a well bore, including continual valve actuation and reduction or elimination of valve tripping.